XVII Changes of Birth and Death Rates and Their Demographic Effects Nathan Keyfitz Present rates of birth and death are unstable: they cannot stay as they are. When change occurs, it will have determinable effects, for instance on age distribution. This paper is devoted mainly to examining the effects of changes in rates of birth at specific ages of mothers and death at specific ages on the overall rate of increase of populations and on their age distributions. It is introduced by a brief survey of rates of birth and death in the world according to recent data on which newly computed life tables and other results have been produced. SUMMARY An analysis of the great mass of data available on contemporary national births and deaths suggests three population types: (a) high birth and high death rates, mainly in Africa; (b) high birth and low death rates, mainly in Asia and Latin America; and (c) low birth and low death rates, among peoples of European ancestry and in Japan. Continuation of this pattern into the future implies a striking change in relative numbers on the different continents, an even greater divergence than exists today in levels of living, and a deterioration of the environment in both rich and poor continents. To achieve a stationary population, imposed by the finite area and resources of the planet, either death rates will rise or birth rates will fall. On the optimistic assumption that the needed adjustment will be by birth rates and on the even more optimistic, extreme assumption that birth rates fall imrne- Nathan Keyfitz is Professor of Demography, University of California at Berkeley. Thp. rp.senrcli behind this chanter has been supported by NSF grant GZ995, by NIHnference of the Industrial Council for Tropical Health, October 1969, Harvard School of Public Health, Boston, Mass.